Production of photographic color images



Patented May 25, 1943 PRODUCTION OF PHOTOGRAPH) COLOR IMAGES Alan Gilbert Tull, Parley, England, assignor to Latta Syndicate Hmited, London, England, a

British company No Drawing.

Application February 10, 1941, Se-

rial No. 318,302. In Great Britain February 22,

The present invention relates to the production of colored photographic images and more particularly to the production of diflferently colored images at different depths of a photographic silver halide emulsion or in the diiIerent layers of a photographic element having two or more superposedemulsion layers.

The production of colored photographic images by the conversion of an image deposit into a colored metal salt or metal compound or complex, is well known, such processes being known as "chemical toning."

It has been discovered that if images are first formed which consist of an intermediate substance in the formation of the final color images while the remainder of the layer consists of silver or a silver salt which is not converted along with theintermediate' substance, the final color images tend to be deposited in separate layers or strata of the emulsion if a mixed toning bath, that is one which contains reagents for producing a plurality of. colored deposits from the intermediate substance, is used.

Thus to take a specific example, if an emulsion layer containing a silver ferrocyanide deposit representing an image and a complementary deposit of silver or silver halide, is treated in a toning bath containing a ferric salt and a uranium salt, a Prussian blue image is formed in the surface stratum and a uranium ferrocyanide image below. The phrase complementary deposit implies a deposit in those portions of the layer not occupied by the intermediate substance.

The silver ferrocyanide or other intermediate image deposit may either be produced from the silver developed from the latent image or from the residual halide after development of the latent image to silver. In the former case a colored negative is produced as a result of a camera exposure while in the latter case a positive image is formed by reversal, but in either case it is important that the intermediate image deposit is surrounded by a complementary image deposit, which may be the residual halide in the former case and the developed silver in the latter case.

This procedure ofiers the possibility of producing differently colored component images for color photography and the principal object of the present invention is to provide a method of pro- 6 Claims.

ducing such colored images which is simple and cheap to operate.

In accordance with the present invention a method of producing differently colored images at different depths of a photographic silver halide emulsion or of an element including several superimposed emulsion layers, includes the step of treating an intermediate image, surrounded by a complementary image which is unaffected by the following bath, in a solution containing different toning reagents whereby the dififerent toned products are deposited in different depths of the emulsion or in different layers of emulsion.

The toning baths which are preferably used contain a ferric salt and a uranium salt as active toning reagents. They also contain potassium bromide and nitric acid and the proportion of the components of the toning bath has a marked effect on the. depths at which toning is effected irrespective of the period of treatment and by suitable control of the constituents of the mixed bath the zone of formation of the Prussian blue may be made co-extensive with the outer layer or stratum which may be sensitised to. record a particular color range while the zone of formation of the uranium salt image may correspond to an under layer or stratum sensitive to another color range, thus enabling a multi-color image to be produced.

In the following example it will be assumedthat an orthochromatic, thin-film emulsion has been sensitised for red for part of its depth "and contains a red or other filter dyestuif to prevent blue and green light from passing into the red sensitive part of. the layer when the element is exposed through the support. After exposure in this manner to produce latent images representing different color aspects of the photographed object, and assuming a reversed, natural color record is required,'the element is developed and without fixing the residual halide is converted into an intermediate image deposit without removing the developedsilver. Conveniently the intermediate image consists of silver ferrocyanide and it may be produced as described in my copending application Serial No. 378,301, filed February 10, 1941, which gives an intermediateimage of a silver ferrocyanide complex which reacts similarly to normal ferrocyanide. The following toning bath is given by way of example as it has been found suitable for the toning of an element produced in the manner indicated but it will be appreciated that the proportions of the reagents in the bath will have to be varied to some extent to suit the sensitisation or other characteristics of the element.

Cubic centimeters Percent solution 53 ONOIIb This bath produces a blue image by reaction of the ferric nitrate with the silver ferrocyanide and a red image by reaction of the uranium nitrate with the silver ferrocyanide. During a period of treatment of from five to as much as 30 minutes, the blue image is restricted to the surface stratum while the red image is formed in the lower part of the layer.

If the silver ferrocyanide in the two strata represents different color aspects of a photographed subject, for instance as a result of the differential I sensitisation of the strata, the \blue and red images comprise component color images, together recording the colors of the original subject.

The foregoing example represented the application of the invention to reversal processes but it may also be applied to negative or non-reversal processes in which after development of the latent images to silver, the latter is converted into an intermediate deposit conveniently of silver ferrocyanide without removal of the unaffected silver halide. This step is conveniently performed in a ferricyanide bleach bath such as the following:

. ccs. Potassium ferricyanide, solution -6 Ammonia, 10% of .880 solution 6 Water t 30 after which the layer is washed.

The next step is to treat the element in a mixed toning bath such as that given in the foregoing example.

After toning and washing, the final step in either example is the removal of unwanted silver orsilver halide for instance with Farmers reducer or with acid-hypo if silver salts only are present. In place of Farmer's reducer the following modified formula is preferred.

A. Potassium ferricyanide per cent 10 B. Hyp am 20 Sodium acetate gm.. 1 Acetic acid 10% cc 1 Water in cc 100 One part of A is mixed with three or four parts of B immediately before use.

images, to coloring operations as described herein.

Furthermore although the invention has been specifically described as applied to the production of two diflerent colors in two different strata or layers, the same principles are applicable to the differential coloring of three or more layers or strata. Thus a layer or layers containing silver ferrocyanide intermediate images might be toned in a solution containing a ferric salt, a uranium salt and a lead salt. The ferric salt produces a blue image which lies at the surface; below this is a red image produced from the uranium salt while below that a lead ferrocyanide image is formed which may be toned yellow by a chromate solution in the well known manner.

I claim: 7

1. A method of producing differently colored images at different depths of a photographic silver halide emulsion coat which includes the steps of producing image deposits of silver ferrocyanide representing different color values at different depths in said coat, said image deposits being surrounded by a complementary deposit of silver or a silver salt which is unaffected by the following bath, and treating the emulsion coat in a bath containing a ferric salt and a uranium salt to produce from the silver ferrocyanide a Prussian Blue image in the surface of the coat and anranium ferrocyanide image below.

2. A method of producing differently colored reversal images at different depths of a photographic silver halide emulsion coat which includes the steps of developing latent images representing different color values at different depths in said coat, producing intermediate image deposits of silver ferrocyanide from the unaffected halide in said coat without removing the developed latent image silver, and treating the emulsion coat in a bath containing a ferric salt and a uranium salt to produce a.Prussian Blue image in the surface of the coat and a uranium ferrocyanide image below.

3. A method of producing differently colored images at different depths of a photographic silver halide emulsion coat which includes the steps of developing latent images in said coat representing different color values at different depths, converting the developed images. into silver ferrocyanide without affecting the residual halide, and treating the coat in abath containing a ferric salt and a uranium salt to form a blue image in the surface and a red image below, said image forming a negative record of the photographed object.

4. A method of producing differently colored images at different depths of a photographic silver halide emulsion coat which includes the steps of developing latent images in said coat representing different color values at different depths, converting the developed images into silver ferrocyanide without removing the residual halide, and treating the coat in a bath containing a ferric salt, a uranium salt, nitric acid and potassium bromide, the proportions of which are controlled so as to deposit a blue image in a desired surface portion of the coat and a red image below.

5. A method of producing diiferently colored reversal images at diiferent depths of a photographic silver halide emulsion coat which in- .cludes the steps of developin latent images in said coat representing different color values at different depths, producing an intermediate image deposits of silver ferrocyanide from the unaffected halide in said coat without removing the developed silver, and treating in a toning bath containing a ferric salt, a uranium salt, nitric acid and potassium bromide, the relative proportions of which are approximately one, four, five and two parts respectively, to deposit a blue image in a desired surface portion of the coat and a red image below.

6. A method of producing three difierently colored images at three diflferent depths of a photographic silves halide emulsion coat which includes the steps of producing intermediate image deposits of silver ferrocyanide in said coat representing different color values at diiferent depths and surrounded by a. complementary deposit which is unafiected by the following bath, and treating the emulsion coat ina bath containing a ferric salt, a uranium salt and a. lead salt to produce a blue image at the surface, followed by a red image with a lead ferrocyanide image below 10 the redimage.

ALAN GILBERT TULL. 

